(1) Field of the Invention
The present invention relates to a distance control apparatus for an automotive vehicle in which a distance between the vehicle and a preceding vehicle is controlled by adjusting a vehicle speed using a throttle adjusting actuator and a brake actuator, so that the vehicle is kept away from the preceding vehicle at a controlled distance when the vehicle is operating in an automatic speed control mode.
(2) Description of the Related Art
As disclosed in Japanese Laid-Open Patent Application No. 60-131327, there is known a distance control apparatus of an automotive vehicle in which a distance between the vehicle and a preceding vehicle is controlled by detecting the distance and controlling a speed of the vehicle through adjustment of a throttle opening angle of a throttle valve in the vehicle.
Hereinafter, for the sake of convenience of description, a vehicle including a distance control apparatus will be referred to as the vehicle, and a preceding vehicle will be referred to as the target, and a distance between the vehicle and a preceding vehicle will be referred to as a following distance.
In the apparatus of the above-mentioned publication, a following distance between the vehicle and the target is detected by using a distance detecting device, and a speed of the vehicle is detected by using a vehicle speed sensor. A safe distance appropriate for the speed of the vehicle is calculated. A speed of the target is calculated from the following distance and the speed of the vehicle. When the distance from the vehicle to the target changes and exceeds a given distance, a vehicle speed holding signal is supplied for a given time period so that the speed of the vehicle is retained by the vehicle speed holding signal. A ratio of change of the speed of the vehicle needed for changing the following distance to the safe distance is calculated, and a following distance control is performed by controlling the speed of the vehicle in conformity with the ratio of change of the vehicle speed by adjusting the throttle opening angle of the throttle valve.
In the above-described apparatus, if the speed of the target when the vehicle speed hold signal is supplied or after the vehicle speed hold signal has been supplied, is high and a difference in speed between the vehicle and the target exceeds a reference value, the speed of the vehicle is controlled by adjusting the throttle opening angle such that the vehicle is operating at a previous vehicle speed prior to the start of the following distance control.
In the above-described apparatus, the following distance control is automatically stopped or canceled when the conditions related to the vehicle and the target are satisfied, and it is automatically started when the conditions are not satisfied. Therefore, if the conditions are abruptly satisfied or unsatisfied under certain circumstances, the operating condition of the vehicle is abruptly shifted or changed due to the start/stop of the following distance control, and a sudden change in the behavior of the vehicle is given to the vehicle operator. This causes the riding comfort of the vehicle to be degraded. The above-described apparatus is likely to give a sudden change in the behavior of the vehicle to the vehicle operator under certain circumstances.
For example, if the target is concealed by another vehicle from a detectable range of the vehicle when the target is running at a low speed (e.g. 10 km/h) and the vehicle is being decelerated from a high speed (e.g. 50 km/h) in order to keep the vehicle away from the target at a controlled distance by execution of the following distance control, the detection of the distance between the vehicle and the target abruptly becomes impossible. In this case, the following distance control is forcefully terminated by the failure of the detection, and the speed of the vehicle is quickly changed back to the previous high speed due to cancellation of the following distance control. In the above-described apparatus, a sudden change in the behavior of the vehicle is given to the vehicle operator.
Further, there is another case in which the vehicle abruptly approaches the target from a long distance and the target is running at a relatively low speed. In this case, when the following distance becomes less than the given distance, the following distance control is automatically started to reduce the speed of the vehicle. However, if a difference in speed between the vehicle and the target is excessively large, the vehicle is abruptly decelerated by starting the following distance control. In the above-described apparatus, a sudden change in the behavior of the vehicle is given to the vehicle operator.